The present invention relates to a fibrous material-based friction member used as a brake shoe or brake block in automobiles, railroad cars, industrial machines and the like or, more particularly, to a friction member formed by consolidating various kinds of fibrous materials by using a novel resinous binder.
Needless to say, friction members such as brake shoes or brake blocks are indispensable parts in all kinds of traffic vehicles, e.g. automobiles and railroad cars, and many of industrial machines for the braking purpose. These friction members are usually prepared by consolidating various kinds of fibrous materials including inorganic fibers, e.g. asbestos and ceramic fibers, and organic fibers, e.g. fibers of polyimide, polyamide and phenolic resins, by use of a resinous binder with optional addition of fillers and other additives. Performance evaluation of such a friction member is performed in terms of various physical properties at high temperatures including coefficient of friction, amount of wearing by friction, attacking behavior on the metal plate rubbed therewith and creaking as well as mechanical properties such as bending strength and flexibility.
Along with the trend in recent years toward higher and higher speed of all kinds of traffic vehicles, on the other hand, brake shoes or blocks as an application form of friction members are required to have extremely high stability in the braking effect even under severest working conditions in order to ensure safety in traffics. It is generally understood that the performance of a friction member to be evaluated from this standpoint is influenced most strongly by the resinous binder for binding and consolidating the above mentioned fibrous base material into a form.
The resinous binder used in the preparation of a friction member is, in most cases, a thermosetting resin and phenolic resins are widely used in view of their high heat resistance, excellent wearing resistance, good workability and inexpensiveness in comparison with other types of thermosetting resins. Phenolic resins currently used as a binder of friction members are mostly modified with various synthetic resins of other types with an object to obtain further improvements in respect of the above mentioned characteristics.
For example, organopolysiloxanes having a linear-chain molecular structure are proposed in Japanese Patent Kokai No. 55-92738 as a modifier of novolac-type phenolic resins which can be imparted with improved elasticity, propagation of tension and tensile strength when combined with an organopolysiloxane. Modification of a phenolic resin with a linear-chain organopolysiloxane, however, is accompanied by several problems and disadvantages including decrease in the softening point and solvent resistance of the resin and eventual appearance of slipperiness which is quite undesirable for a friction member when cracking of the organopolysiloxane takes place to produce low-molecular organopolysiloxane molecules. Thus, one of the most important technical problems to be solved in the technology of friction members is to develop a resinous binder for the fibrous base materials capable of imparting the friction member with greatly improved heat resistance and wearing resistance without being accompanied by the above mentioned disadvantages in the prior art.